Al 3p valence and excitonic states in GaSb/Al0.3Ga0.7Sb and GaA

Abstract

Density of states ͑DOS͒ in GaSb/Al 0.3 Ga 0.7 Sb systems are studied by electron-induced x-ray emission spectroscopy ͑EXES͒ and compared to previous results we have obtained for GaAs/Al 0.3 Ga 0.7 As systems. The Al 3p valence DOS are analyzed in the bulk ternary compounds, in heterostructures, and in interfacial zones 30 Å thick, this thickness being equivalent to that of heterostructure layers. Large changes of the Al 3 p valence DOS are seen, depending on the preparation conditions of the samples whose quality was checked by photoluminescence. For heterostructures having a small interface roughness, localization of states on the whole valence band of barriers is evidenced. This localization is attributed to bidimensional effects that largely dominate the interface effects. In contrast, for heterostructures having interfaces of lower quality, interface interaction and localization are competitive. Core excitonic transitions seen by EXES confirm that localization of Al states in the barriers exists for superlattices with abrupt interfaces.